1. Technical Field
The present technology relates to a pneumatic tire that is a studless tire having enhanced traveling performance on ice at initial use.
2. Related Art
Pneumatic tires known as “studless tires” have been proposed and put into actual use that have enhanced performance factors such as braking ability on ice and steering stability on snow when traveling on icy and snowy road surfaces.
Some studless tires use tread compounds containing fine protrusions as a filler so as to obtain an edge effect on icy surfaces, and some use rubber including fine voids so as to obtain a water pickup effect and an edge effect.
However, generally, if a rubber layer including the filler and/or microscopic voids is exposed on a tire surface, which directly contacts a mold when vulcanizing/curing the rubber, said rubber layer will not be formed. Therefore, the fillers and voids do not exist in the tread surface at initial use of the tire and the effectiveness of the filler and/or the voids are not displayed, or, even if displayed, a degree of said effectiveness is small.
Therefore, as a studless pneumatic tire capable of displaying high effectiveness at initial use, a pneumatic tire has been proposed including, in a tread surface, a plurality of land portions partitioned by a plurality of main grooves, wherein at least one sipe extending in the tire width direction divides the land portions, thus forming sub-blocks. Furthermore the land portions include a plurality of shallow grooves that are more shallow than the sipes, the shallow grooves extending from a center of the land portions in a water flow direction in the main grooves toward both edges, and where the shallow grooves are open to the main grooves. Open portions of the shallow grooves are positioned more on a downstream side of the flow direction in the main grooves than center portions of the land portions (Japanese Unexamined Patent Application Publication No. 2006-151229).
The subject matter of this proposal seeks to enhance the water pickup effect and edge effect by removing or draining water through a plurality of narrow grooves formed so as to extend in a single direction while inclining in the tire circumferential direction, or, via a plurality of narrow grooves formed so as to extend in two intersecting directions. However, in many cases, the subject matter of this proposal does not sufficiently display water removal or draining as a result of providing the narrow grooves, and thus, cannot be considered to be satisfactory.